This project will consider cell membrane permeability changes that occur concurrent with development of spermatozoa. Both active and passive components of movements of potassium, sodium and chloride will be analyzed using data from measurements of membrane potential, radioisotope determinations of labelled potassium, sodium and chloride in the presence or absence of inhibitors of transport ATPase. Acquisition of motility at the level of the spermatid will be investigated by cinematography and related to the membrane properties in light of previously established membrane characteristics of the mature spermatozoon.